1. Field of the Invention
The present invention pertains to systems and methods for enhancing the hearing of hearing-impaired subjects, and in particular, in the exemplary embodiment to a system and method for enhancing the binaural representation for hearing-impaired subjects.
2. Description of the Related Art
There are two main binaural cues for localizing sound in the plane of azimuth, namely (i) interaural time differences (ITDs), and (ii) interaural level differences (IUDs). ILDs are a high-frequency cue, and occur because a sound that is off to one side of a listener's head is louder at the near ear than it is at the far ear (see FIG. 1 discussed herein). ITDs urea low-frequency cue, and are comprised of very small differences in the time-of-arrival between the two ears when a sound is off to one side.
An auditory environment containing one or more sound sources (talkers or other sources of sound) is often referred to as an auditory scene. Individuals with normal hearing can use the binaural cues discussed above for sound localization to improve speech intelligibility in an auditory scene where one talker (referred to as a target) and a second talker (referred to as a masker) are spatially separated from one another, such as in the well-known “cocktail-party” problem. Such an improvement in speech intelligibility is referred to in the art as a spatial release from masking (SRM).
Although listeners with hearing impairment can often understand speech in quiet settings as well as listeners with normal hearing, they often show dramatic declines in speech understanding in the presence of background noise, A competing talker is often the most challenging type of background noise, and is also the most difficult to ameliorate with typical noise-reduction schemes, More specifically, individuals with hearing impairment show little SRM. As a result, these listeners are less able to make sense of an auditory scene that contains multiple sound sources, and are thus typically unable to understand speech in the presence of noise, such as another talker.
A cochlear implant (CI) is a surgically implanted electronic device that provides a sense of sound to a person having a hearing impairment. In some people, cochlear implants can enable sufficient hearing for better understanding of speech. The quality of sound is different from natural hearing, with less sound information being received and processed by the brain. However, many patients are able to hear and understand speech and environmental sounds.
Implanting both cochleas of hearing-impaired listeners with cochlear implants (referred to as bilateral cochlear implants (BCIs)) has become more common in recent years. However, implantation is invasive, costly, and can potentially destroy any residual hearing in the ear to be implanted. A loss of residual hearing can be detrimental to speech reception, even if the amount of hearing is extremely limited. Thus, it is crucial that clear benefits of BCIs over a single device, with or without the addition of residual hearing, be established to justify the decision to implant the second ear. One often-cited potential outcome of BCI is the ability of such users to perceive and use binaural cues. However, BCI users have thus far shown relatively poor localization abilities and limited SRM. This is likely because BCI users receive limited access to binaural cues. First, they perceive only ILDs and not ITDs. Second, as shown in FIG. 1, robust ILDs are generally restricted to frequencies above about 1500-2000 Hz because the longer wavelengths at lower frequencies are not shadowed by the head. Thus, the binaural representation of BCI users is inconsistent across frequency, and it has been shown that sensitivity. to binaural cues declines with such an inconsistency. In addition, any ILDs that BCI users receive will be subjected to large amounts of compression in the processing electronics of the BCIs. This includes automatic gain control on the processing frontend, which essentially limits the level of more intense sounds, likely reducing ILDs as a result, and the compression that occurs to map the input dynamic range (which is typically 60 dB or less) to the electric dynamic range (typically 10-20 dB).
There is thus a need for an effective system and method for enhancing the binaural representation for hearing-impaired subjects, such as, without limitation, those subject that have BCIs.